If i am planning to get a macro lens for insect shooting, what MFD is ideal? i think that the bigger the MFD, the better? also, in order to achieve 1:1 ratio, it must be shot at the MFD only ? for example, if the MFD is 30cm, in order to get a 1:1 magnification, do i set it to its MFD by adjusting the barrel of the lens, and then slowly move in my camera until the image is sharp...this would be my 1:1 image ?

Thanks

Technically yes. More MFD gives you more working distance (the distance between your camera and the subject). It also prevents your lens from blocking light source.

You have the correct idea of achieving 1:1 magnification too, but I don't think most of us use 1:1 frequently.

That being said, more MFD means longer focal distance. Longer focal distance also makes the lens heavier, bigger, a lot more expensive (just compare Canon 100mm and 180mm then you know) and sometimes harder to use since the focal length is longer and more prone to hand shake.

thanks. when i check a tamron 90mm, it has 30cm MFD, but a non macro 18-55mm, its MFD is even smaller, 25mm.. why then 18-55 could not achieve a 1:1 ? (i thought the closer you can focus, 25mm vs 30mm, the better magnification you will achieve?)

easy question. check the focal length.

One is 90mm and one is 55mm.

Generally a wider angle lens will always have shorter MFD compared to a longer focal length lens. For example a 10mm lens might has 10cm MFD and a 200mm lens has 100cm MFD but they aren't that much difference in magnification

This post has been edited by mingyuyu: Oct 5 2014, 08:06 PM

sorry not 25mm, i meant 25cm.. non macro lens has MFD of 25cm, which means it can focus even nearer than a macro lens, why it cant produce a 1:1 ..? sry ask stupid q

I don't think any non-macro lens can focus nearer than dedicated macro lens
As for dedicated macro lens getting 1:1; yes you usually need to get to the closest distance to get that magnification

that is because the mfd (that is in built on the lens) prevent it from achieving it.. what some does is to use focus bellows or extension rings to reduce the MFD. you can achieve 1:1 even with a 50 mm lens but I will not recommend it of anything of shorter focal length as it will be too close to the lens for it to be of any practical use..

There are other limits for consideration... the further you move the lens away from the focal plane.. the more light is needed also for some lens you will suffer from vignette ie darkening of the edges.. as there is no data there.. because the lens opening is too small..

One very interesting lens you can consider is the Novoflex Novoflexar 400mm. It can get really close for a 400mm lens because the focusing system base on extendable by several cm.. it is an unusual lens due to its follow focus mechanism - focus by compressing a pistol grip (rack and pinion) unlike helicoid in traditional focus.

my bad, i corrected my reply.
there's a lot of lens that can focus nearer than macro lens, typically wide angle lens.

for example my oly 12-40mm at 40mm can focus like 20cm from the subject at MFD to get 0.6x magnification, but the canon 100mm's MFD is at 30cm for 1x magnification.

so does that mean that it is the specialty of a macro lens to achieve 1:1 at its MFD..but for other non macro lens, eventhough the MFD is much smaller, it would not be able to achieve a 1:1 at its MFD?

it seems counter intuitive for me, because, from a layman POV, the closer you can get into an object (oly at 20cm from a bug vs tamron macro at 30cm from the bug), you could see and capture more detail (ie more magnification)...

I got one macro lens to let go, pls check my siggy. Its a sharp lens, f16 would give me sufficient dof compared to when working with Canon 100mm macro (normally I use the max dof at f/22).

In general, short focal length macro lens have short MFD compared to longer macro lens.

small MFD doesn't mean high magnification.

the logic is still the same no matter how it doesn't make sense to you, any lens that has high magnification can be considered as macro lens already, like 0.5x magnification for the Fujifilm 60mm and it's still a macro lens.

higher focal length is the thing that caused further minimum focal distance. you have to read articles around google for super detailed explaination if you still don't understand.